Protist, Vol. 153, 197–220, September 2002 © Urban & Fischer Verlag http://www.urbanfischer.de/journals/protist Published online 13 September 2002 In the last decades, research on photosynthetic pro- cesses has evolved with the development of molec- ular and structural techniques. Today, we can draw molecular pictures of many of these processes in great detail. The genome projects on photosynthetic model organisms, like Arabidopsis (the entire genome has been sequenced) and the green alga C. reinhardtii (more than 135000 EST sequences have been obtained and the complete genome sequence is presumably available by fall 2002), will be of enor- mous help to further elucidate aspects of assembly, function and regulation in photosynthesis com- plexes. To proceed in these research lines, C. reinhardtii, also referred to as the green yeast (Rochaix 1995) will be an important tool. In recent years, the power- ful techniques of molecular genetics and the estab- lishment of methods for nuclear or chloroplast transformation (see below) in C. reinhardtii have greatly increased the potential of this system for an- alyzing bioenergetic processes (Hippler et al. 1998a; see below). Studies with C. reinhardtii have led to significant advances in our understanding of the as- sembly of photosynthetic complexes (see Fig. 1) and of the structure-function relationship of their components. The Use of C. reinhardtii as a Tool to Dis- sect Processes that Affect Assembly and Regulation of Photosynthetic Complexes Basic Features An important feature of C. reinhardtii is that cell growth and survival do not solely depend on photo- synthesis, when a carbon source such as acetate is added to the growth medium. Numerous nuclear and chloroplast photosynthetic mutants have been isolated, taking advantage of acetate requirement for growth or fluorescence analysis. Fluorescence analysis can be used as a non-invasive method to distinguish between wild-type and mutant pheno- types. This approach can also be applied to live cells. The analysis is based on the observation that mutants deficient in photosynthetic activity exhibit altered fluorescence properties (Delepelaire and Bennoun 1978) and led to the discovery of both high and low fluorescence mutants. Using this method it was possible to isolate photosynthetic mutants that are deficient in PSII, PSI and cyt b 6 f complexes (see Hippler et al. 1998a; Rochaix 2001). Like land plants, C. reinhardtii contains three dis- tinct genetic systems located in the nucleus, chloro- plast and mitochondria respectively. Nuclear genes follow a typical Mendelian 2:2 segregation whereas chloroplast or mitochondrial mutations are predomi- nently inherited from the mating-type (+) or (–) par- ent, respectively (see Harris 1989). Thus, mutations in each of these genomes can be distinguished ge- netically. In addition, technologies for chloroplast and nuclear transformation have been established for C. reinhardtii. Chloroplast and Nuclear Transformations The establishment of the methodology for chloro- plast transformation by Boynton et al. (1988) al- lowed extensive chloroplast gene manipulation. In this biolistic transformation procedure, DNA is pre- cipitated on tungsten particles that are bombarded onto cells with a particle gun. When the DNA is intro- duced into the chloroplast compartment, the trans- forming DNA is integrated into the chloroplast Photosynthetic Complex Assembly in Chlamydomonas reinhardtii PROTIST NEWS Abbreviations: ATP, adenosine tri-phosphate; Chl, chlorophyll; cyt, cytochrome; LHC, light-harvesting complex; OEC, oxygen evolving complex; MS, mass spectrometry, pc, plastocyanin; P 700 , primary electron donor in PSI; P 680 , primary electron donor in PSII; PSI, photosystem I; PSII, photosystem II; PQ, plasto- quinone; RC, reaction center; SDS-PAGE, sodium do- decyl sulphate-polyacrylamide gel electrophoresis Protist 1434-4610/02/153/03-197 $ 15.00/0